1. Field of the Invention
This invention relates to mobile machinery for driving posts into the ground for the construction of fences, safety barriers, guard railing, retaining walls, or like constructions. It is intended as a substitute for hole digging, fill, and tamping apparatus.
2. Related Prior Art
For many decades the customary approach to the building of fences involved the digging of holes of appropriate depth, the placement of the post therein, and filling of the surrounding hole with removed soil and tamping to stabilize the emplaced post, all of which required much manual labor. Then came angle and "Tee" metal posts, or small cross section, that could be driven in place by hammer or manual driving tools. But posts, having large cross sections are still desired for many decorative and utilitarian applications, including fences about lawns and pastures for horses, and for safety barriers, etc. A long standing need has existed for efficient labor saving apparatus for setting posts upright in all types of soils and upon terrain having variable slopes and contours.
An early mobile post driver is disclosed in U.S. Pat. No. 2,940,267, issued to Shaver in 1960. Shaver teaches a percussion driver, that is, a hydraulic system to lift a mechanical mass of a driving block and H beam above the post so that upon release of hydraulic pressure gravity will provide a driving force to set the post in the soil without the need for digging or filling post holes. The device of Shaver is intended for mounting on the longitudinal axis of a tractor of the row crop type generally used in agricultural operations. Mechanical adjustments were provided for vertical driving of the post, however the location of the post at a desired place required accurate maneuvering of the tractor.
In a less demanding allied area, the U.S. Pat. No. 3,563,319, issued to Nixon in 1971 teaches apparatus for the setting of small pins or stakes in concrete forms used in highway construction. Since the concrete form must follow the slope of the graded roadbed the only need for verticality adjustment is in the lateral direction to the roadway. The setting of pins is accomplished by hydraulic force rather than by gravity action on hammer mass. Verticality of the applied force is adjusted by a hydraulic lateral tilting of the chassis of the platform which is supported by three wheels, two of which are arranged longitudinally and the third being offset laterally from the two.